libgo/go/encoding/hex/hex.go

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Package hex implements hexadecimal encoding and decoding.
   6 package hex
   7
   8 import (
   9         "bytes"
  10         "errors"
  11         "fmt"
  12         "io"
  13 )
  14
  15 const hextable = "0123456789abcdef"
  16
  17 // EncodedLen returns the length of an encoding of n source bytes.
  18 func EncodedLen(n int) int { return n * 2 }
  19
  20 // Encode encodes src into EncodedLen(len(src))
  21 // bytes of dst.  As a convenience, it returns the number
  22 // of bytes written to dst, but this value is always EncodedLen(len(src)).
  23 // Encode implements hexadecimal encoding.
  24 func Encode(dst, src []byte) int {
  25         for i, v := range src {
  26                 dst[i*2] = hextable[v>>4]
  27                 dst[i*2+1] = hextable[v&0x0f]
  28         }
  29
  30         return len(src) * 2
  31 }
  32
  33 // ErrLength results from decoding an odd length slice.
  34 var ErrLength = errors.New("encoding/hex: odd length hex string")
  35
  36 // InvalidByteError values describe errors resulting from an invalid byte in a hex string.
  37 type InvalidByteError byte
  38
  39 func (e InvalidByteError) Error() string {
  40         return fmt.Sprintf("encoding/hex: invalid byte: %#U", rune(e))
  41 }
  42
  43 func DecodedLen(x int) int { return x / 2 }
  44
  45 // Decode decodes src into DecodedLen(len(src)) bytes, returning the actual
  46 // number of bytes written to dst.
  47 //
  48 // If Decode encounters invalid input, it returns an error describing the failure.
  49 func Decode(dst, src []byte) (int, error) {
  50         if len(src)%2 == 1 {
  51                 return 0, ErrLength
  52         }
  53
  54         for i := 0; i < len(src)/2; i++ {
  55                 a, ok := fromHexChar(src[i*2])
  56                 if !ok {
  57                         return 0, InvalidByteError(src[i*2])
  58                 }
  59                 b, ok := fromHexChar(src[i*2+1])
  60                 if !ok {
  61                         return 0, InvalidByteError(src[i*2+1])
  62                 }
  63                 dst[i] = (a << 4) | b
  64         }
  65
  66         return len(src) / 2, nil
  67 }
  68
  69 // fromHexChar converts a hex character into its value and a success flag.
  70 func fromHexChar(c byte) (byte, bool) {
  71         switch {
  72         case '0' <= c && c <= '9':
  73                 return c - '0', true
  74         case 'a' <= c && c <= 'f':
  75                 return c - 'a' + 10, true
  76         case 'A' <= c && c <= 'F':
  77                 return c - 'A' + 10, true
  78         }
  79
  80         return 0, false
  81 }
  82
  83 // EncodeToString returns the hexadecimal encoding of src.
  84 func EncodeToString(src []byte) string {
  85         dst := make([]byte, EncodedLen(len(src)))
  86         Encode(dst, src)
  87         return string(dst)
  88 }
  89
  90 // DecodeString returns the bytes represented by the hexadecimal string s.
  91 func DecodeString(s string) ([]byte, error) {
  92         src := []byte(s)
  93         dst := make([]byte, DecodedLen(len(src)))
  94         _, err := Decode(dst, src)
  95         if err != nil {
  96                 return nil, err
  97         }
  98         return dst, nil
  99 }
 100
 101 // Dump returns a string that contains a hex dump of the given data. The format
 102 // of the hex dump matches the output of `hexdump -C` on the command line.
 103 func Dump(data []byte) string {
 104         var buf bytes.Buffer
 105         dumper := Dumper(&buf)
 106         dumper.Write(data)
 107         dumper.Close()
 108         return string(buf.Bytes())
 109 }
 110
 111 // Dumper returns a WriteCloser that writes a hex dump of all written data to
 112 // w. The format of the dump matches the output of `hexdump -C` on the command
 113 // line.
 114 func Dumper(w io.Writer) io.WriteCloser {
 115         return &dumper{w: w}
 116 }
 117
 118 type dumper struct {
 119         w          io.Writer
 120         rightChars [18]byte
 121         buf        [14]byte
 122         used       int  // number of bytes in the current line
 123         n          uint // number of bytes, total
 124 }
 125
 126 func toChar(b byte) byte {
 127         if b < 32 || b > 126 {
 128                 return '.'
 129         }
 130         return b
 131 }
 132
 133 func (h *dumper) Write(data []byte) (n int, err error) {
 134         // Output lines look like:
 135         // 00000010  2e 2f 30 31 32 33 34 35  36 37 38 39 3a 3b 3c 3d  |./0123456789:;<=|
 136         // ^ offset                          ^ extra space              ^ ASCII of line.
 137         for i := range data {
 138                 if h.used == 0 {
 139                         // At the beginning of a line we print the current
 140                         // offset in hex.
 141                         h.buf[0] = byte(h.n >> 24)
 142                         h.buf[1] = byte(h.n >> 16)
 143                         h.buf[2] = byte(h.n >> 8)
 144                         h.buf[3] = byte(h.n)
 145                         Encode(h.buf[4:], h.buf[:4])
 146                         h.buf[12] = ' '
 147                         h.buf[13] = ' '
 148                         _, err = h.w.Write(h.buf[4:])
 149                         if err != nil {
 150                                 return
 151                         }
 152                 }
 153                 Encode(h.buf[:], data[i:i+1])
 154                 h.buf[2] = ' '
 155                 l := 3
 156                 if h.used == 7 {
 157                         // There's an additional space after the 8th byte.
 158                         h.buf[3] = ' '
 159                         l = 4
 160                 } else if h.used == 15 {
 161                         // At the end of the line there's an extra space and
 162                         // the bar for the right column.
 163                         h.buf[3] = ' '
 164                         h.buf[4] = '|'
 165                         l = 5
 166                 }
 167                 _, err = h.w.Write(h.buf[:l])
 168                 if err != nil {
 169                         return
 170                 }
 171                 n++
 172                 h.rightChars[h.used] = toChar(data[i])
 173                 h.used++
 174                 h.n++
 175                 if h.used == 16 {
 176                         h.rightChars[16] = '|'
 177                         h.rightChars[17] = '\n'
 178                         _, err = h.w.Write(h.rightChars[:])
 179                         if err != nil {
 180                                 return
 181                         }
 182                         h.used = 0
 183                 }
 184         }
 185         return
 186 }
 187
 188 func (h *dumper) Close() (err error) {
 189         // See the comments in Write() for the details of this format.
 190         if h.used == 0 {
 191                 return
 192         }
 193         h.buf[0] = ' '
 194         h.buf[1] = ' '
 195         h.buf[2] = ' '
 196         h.buf[3] = ' '
 197         h.buf[4] = '|'
 198         nBytes := h.used
 199         for h.used < 16 {
 200                 l := 3
 201                 if h.used == 7 {
 202                         l = 4
 203                 } else if h.used == 15 {
 204                         l = 5
 205                 }
 206                 _, err = h.w.Write(h.buf[:l])
 207                 if err != nil {
 208                         return
 209                 }
 210                 h.used++
 211         }
 212         h.rightChars[nBytes] = '|'
 213         h.rightChars[nBytes+1] = '\n'
 214         _, err = h.w.Write(h.rightChars[:nBytes+2])
 215         return
 216 }